Spherical acoustic transducer

ABSTRACT

A spherical acoustic transducer formed from electromechanically active material and having a common electrode attached to one surface as a voltage reference and a distribution of electrodes attached to other surfaces so that the radial and circumferential vibrating modes of the acoustically excitable sphere are detectable and resolvable as to bearing angle over 4 pi steradians.

mite States Ehrlich 51 May 8,1973

[54] SPHERICAL ACOUSTIC TRANSDUCER [75] Inventor: Stanley L. Ehrlich,Middletown, R.l.

[73] Assignee: Raytheon Company, Lexington,.

Mass.

[22] Filed: Aug. 15, 1969 [21] Appl. No.: 850,478

[52] U.S. Cl ..340/10, 340/6 [51] Int. Cl. ..G0lv 1/00 [58] Field ofSearch ..340/l0, 6

[56] References Cited UNITED STATES PATENTS 2,565,158 8/1951 Wi11iams.....340/1O UX 2,939,970 6/1960 Dranete et a1. ..340/1O X 2,966,656 12/1960Bigbie et al ..340/1O 3,221,296 11/1965 Milne ..340/1O 3,444,508 5/1969Granfors et al ..34l)/1O X Primary Exa minerBenjarn'in A. BorcheltAssistant Examiner-H. J Tudor Att0rney-Harold A. Murphy and Joseph D.Pannone [57] ABSTRACT A spherical acoustic transducer'formed fromelectromechanically active material and having a common electrodeattached to one surface as a voltage reference and a distribution ofelectrodes attached to other surfaces so that the radial andcircumferential vibrating modes of the acoustically excitable sphere aredetectable and resolvable as to bearing angle over 41r steradians.

17 Claims, 7 Drawing Figures l as l INS ms) I SPHERICAL 90 commas/non I5 ROTATION OF SUMMING 92 AXIS ciRculTs [Ta 5 OPTIONAL (re) 96 1 5 SLOPE0mm PHASE CORRECTION REE PHASE SHIFT 1 S l as l l h zmmwssi PATENTEDHAY181913 3, 7 32 53 5 sum 1 BF 3 Z=rCOS9 FIG 2 11 x r snveaoscp INVENTOI?STANLEY L. EHRL/CH Wm lei/Wa ATTORNEY PATENTED HAY I 8|975 sum 2 or 3F/Gl 4 INVENTOI? STANLEY L EHRL ICH ATTORNEY BACKGROUND OF THE INVENTIONThis invention relates to spherical acoustic transducers and, moreparticularly, to the utility of such transducers for resolving bearingangle of incident acoustic waves over 411- steradians.

In the prior art, as for example Underwater Acoustics Handbook by V. M.Albers, Penn. State University Press, 1965, LC. 64-15069, at page 157,only fleeting reference is made to the use of a sphere shaped acoustictransducer. While the spherical transducer has been discussedtheoretically as an acoustic radiator, i.e., P. M. Morse in Vibrationsand Sound, published by McGraw-Hill Book Company, New York, in 1936,pages 240-255, such transducers when reduced to practice were limited tothe radial mode of vibration. This limitation in the art derived fromthe number and placement of electrodes. Typically, one outer surface andone internally placed electrode were used.

Non-spherically shaped transducers vibrating in two modes have beenreported. Reference may be made to Stanley L. Ehrlich et al., US. Pat.Nos. 3,176,262 and 3,290,646 issued on Mar. 30, 1965 and Dec. 6, 1966,respectively. In these patents, cylindrically shaped transducers wereemployed for obtaining azimuth and elevation angle bearings. When suchcylindrical transducers were used as a set of four, it was possible todetermine two angles. However, only one angle was available from thebasic single cylinder. As described with multiple cylindrical elements,it was possible to divide them into two or more groups to get the secondangle. However, the beam patterns in the second direction were frequencydependent. Additionally, the cylindrical transducers had a cardioid typebeam directionality, the notches of which form a limitation on thesystem sensitively. A related pattern appears in the magnetostrictivetransducer'of R. L. Peek, U.S. Pat. No. 2,468,837, issued May 3, 1949 atFIGS. 7 and 8.

SUMMARY OF THE INVENTION it is, accordingly, an object of this inventionto devise an acoustic transducer having a spherical shell formed fromelectromechanically active material in which at least two or morevibrating modes of the shell may be utilized for acoustic signalprocessing purposes.

It is a related object to devise a spherical acoustic transducer adaptedto discriminate among bearing and elevation angles over 411' steradians.It is still another object of this invention to devise a sphericalacoustic transducer which may be utilized for moderate to deep watercommercial and research applications over a wide range of signal levelsand in applications where separation of multipath arrivals by angle isof importance.

The above-mentioned objects are satisfied in one embodiment comprising aspherical shell formed from electromechanically active material; aplurality of electrodes attached to the shell outer surface andregularly spaced over equal area segments thereof; another electrodeconnected to the shell inner surface to provide a common voltagereference point; and combining means coupling the outer electrodes andinner electrodes for generating n orthogonally phased output dipoledvoltages and an omnidirectional pattern voltage upon vibration of thespherical shell.

The even distribution of the outer shell electrodes permits thedetection of the electrical manifestations of both the radial mode andthe circumferential mode of vibration inducible in the spherical shell.Furthermore, the multimode shell vibration is detectable independent ofthe incident acoustic signal bearing angle anywhere within 411steradians.

In another embodiment, the shell is divided into a plurality ofelemental surface areas such as two hemispheres connected at itselemental surface areas boundaries by a common metallic locus. Themetallic locus serves as a common voltage reference line. Here, as inthe first embodiment, a plurality of electrodes are attached to theshell outer surface and regularly spaced over equal area segmentsthereof. This type of construction has particular advantage of ease ofmanufacture because hemispheres rather than complete spheres need befabricated.

Another embodiment may be formed by dividing the spherical shell into aplurality of elemental surface areas such as octants. A pair ofelectrically insulated electrodes is assigned to each elemental area,with one electrode of each pair serving as a reference voltage point.The other electrode is subjected to a positive biasing voltage. A commonelectrode is attached to the shell inner surface for maintaining asubstantially radial electric field. This embodiment offers a reducedinterelectrode capacitance between each surface electrode pair. Thecapacitance reduction enables the design of preamplifier-s to meet lownoise requirements.

All of the embodiments would serve to increase the pressure capabilityand improve the pressure release design which would become internal tothe sphere. Furthermore, reversibility of the multimocle effect and itsuse as a transmitter in the light of the teachings of the disclosureshould not present any difficulties. In-

deed, in the transmission context, beam directivity may be improved byreducing beam width through the capacity to concentrate readilyvibration energy from different modes into a narrow beam.

The foregoing aspects and advantages of the invention as well asadditional aspects thereof will be understood more clearly and fullyfrom the description of the preferred embodiments taken with referenceto the accompanying drawing of which the following is a briefdescription.

BRIEF DESCRIPTION OF THE DRAWINGS tant inner electrodes and two outerelectrodes per octant.

FIG. 5 shows the spherical transducer with attached electrodes incombination with the combining means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1A and1B of the drawing, there are shown the extensional vibration patternsfor cylinders and spheres in the zero and first vibration modes. Thezero and first order terms of the Bessel function series expansion ofplane waves interacting with a cylindrical or spherical obstacle are theprincipal ones associated with the multimode transducer configurationsto be subsequently described. As previously mentioned, the vibrationmodes of interest are primarily extensional. For the cylinder, thevibration may be represented as in FIG. 1A. The solid lines 1 and 3 arethe neutral positions of the inner and outer walls respectively. Thedashed lines 2 and 4 are their instantaneous positions at another time.

In FIG. 18, if the figure is viewed as representing the cross section ofa cylinder, then its vibration in the n 1 mode is twofold degenerate(sin (b and cos (b). This plan view is the same for all planes normal tothe cylinder axis. Since there is vibration along one nodal diameter,then this is determinative of the order of the vibration mode. If aspherical shell is substituted for the cylinder in FIG. IE, it also maybe made to vibrate in the m 1 mode. For a sphere, such a vibration modeis three-fold degenerate (cos 0, sin 6 sin dz, and sin 0 cos 4)). Inthis regard, FIG. 18 represents the view of a figure of revolution abouta diametrical axis through the direction of maximum radial displacement.Relatedly, the trace diameter of the one nodal plane is perpendicular tothe axis of symmetry.

Referring now to FIG. 2A of the drawing, there is shown a sphericalmultimode transducer framework with three normally intersecting circularrings. Rings 7,

8, and 9 are shown mutually orthogonal and intersecting at points 10through 15. The three normally intersecting circular rings have equalradii and a common center 16. They support eight identical sphericalshell octants of electromechanically active material such as bariumtitanate (BaTiO Each of the octants is securely, i.e., acoustically,attached to respective octant boundaries. The individual octants may bepolarized identically with the positive potential on the inner sphericalsurface. Each of the inner spherical surface electrodes may beelectrically connected. to the metal framework prior to the octant beingmechanically attached. This provides a common ground for all octants.The common ground may be brought out through the metal framework. Theelectrodes attached to the outer surface for each octant become thesignal leads required to form the basic beam pattern.

Referring now to FIG. 3, there is shown a simpler mechanicalconfiguration using a single metal ring and two hemispheres (only one ofwhich, 17, is shown). The inner electrodes 18 of each hemisphere may becontinuous and connected to the metal ring 19 as a common ground. Thefour outer electrodes 20 (only one of which is shown) are electricallyinsulated from each other. It is possible to have a small hole in thespherical assembly of the two hemispheres cut through so that a wire maybe connected to the inner electrodes 18.

Referring now to FIG. 4 of the drawing, there is shown a hemisphere 17in which a single octant of the sphere divides the'outer electrode intotwo equal electrode areas. The octant, which is, of course, formed fromelectromechanically active material, is polarized by the application ofa positive voltage to one of the outer electrodes with the use of theother outer electrode as a ground. The inner electrode 21 serves as aninaccessible center tap so that the electric field is effectively radialand the capacitance C between the two outer electrodes is, at maximum,one-fourth the capacitance C plus C between the two outer electrodesconnected electrically and the inner electrodes. Illustratively, Crepresents the capacitance between the first outer electrode and theinner electrode. C is the capacitance between the inner electrode andthe other outer electrode. C and C are serially connected. Thus, C (C C/C -i-C If C C then C C /2 C /2 (C, C /4). Each of the eight octants maybe characterized by a high outer electrode, a ground outer electrode,and a floating inner electrode. The inner electrodes for each quadrantshould be isolated from each other. They do not have any externalconnection. The ground outer electrodes for each quadrant may beconnected together to form a common ground. The eight high outerelectrodes will yield the required signals. Note, of course, that theimpedance levels are higher as well as the sensitivity because of theseries connection of the half octants. Mechanical fabrication of thesphere may be in any of the forms for which the inner electrode isrequired. If it is not possible to separate the inner electrode intooctants, then cross talk may be minimized by making the outer groundelectrode substantially larger than the outer high electrode.

Referring now to FIG. 5 of the drawing, there is shown a sphericaltransducer with attached electrodes terminating in a combining means. Inthis regard, spherical transducer 50 is coupled to combining means 52over paths 54, 56, 58, 60, 62, 64, 66, 68.

The combining means comprises a plurality of amplifiers 70, 72, 74, 76,'78, 80, 82, and $4 and summing circuits. Summing circuits 86 terminatethe amplifiers and their corresponding electrical paths for purposes offorming four directional signals on paths 83, 90, 2, 1100 that areorthogonal in the form of voltages that are all in phase or out of phasewith each other. Three directional signals labelled NS, EW, and TB, arerespectively applied over paths 88, 90, and Q2 to a sphericalcompensator 94. An omnidirectional phase reference is applied on path 96to a slope correction phase shift circuit 98 to obtain the desiredrelative phase at 100.

The resonant modes of spherical shell 50 can be used to produce amultimode system. The sphere is divided into hemispheres for all threeorthogonal axes. The bearing angle information is obtained by thesimultaneously appropriate summing of the output 8 octants of thesphere. It is, of course, possible to use basic multimode displays suchas used with cylinder systems found, for example, in US. Pat. No.3,176,262. Spherical compensator 94 with linkages or external frictiondrive may be used to allow maximum rotation for rotating the effectiveaxes of a hydrophone for target tracking or to compensate for roll,pitch, and yaw of a ship or platform.

The beam patterns of shell 50 in multimode are insensitive to frequencybecause they are dependent only on the specific orthogonal modes forwhich the shell is designed and are capable of a complete 4w solid anglecoverage. The signals appearing on lines 54, 56, 58, 60, 62, 64, 66, and68 may be characterized as voltages responsive to the modal vibrationsincurred by the corresponding octant transducer sections. For purposesof relating the voltage signal on a particular line to the compassorientation of the vibrating octant, the leads have also been designatedrespectively as NE, NW, etc. It will be noted that the first four leads54, 56, 58, and 60 represent the top hemisphere octants while theremaining four leads 62, 64, 66, and 68 represent the bottom hemisphereoctants. These may be appropriately designated top T and bottom B withrespect to compass and tilt sensor orientation. Such top and bottomdesignation also provides a complete solid angle orientation.

The signals on each of these lines represent complex magnitudes. Morespecifically, the radial vibration component of the sphere R and thecircumferential vibration component of the sphere C are each complexmagnitudes distributed among the octants such as R/8 and C/8 may beconsidered representative values for the octant in question for purposesof description. Measurements have shown that the relationship between Rand C is itself substantially orthogonal and may be represented as acomplex quantity. Accordingly, the signals appearing on each of thelines 54 through 68 may be represented as follows:

Top NE (R/8) +j (C/8) (sin cos (b sin 0 sin cos 0) Top SW (R/8) +j (C/8)(sin 0 cos d; sin 6 sin e:

+ cos 0) 7 Top NW (R/8) +j (C/8) (sin 0 cos (i) -sin 0 sin (b cos 0)Bottom NE (R/8) +j (C/8) (sin 0 cos 4; sin 0 sin b cos 0) Bottom SE(R/8) +j (C/8) (sin 6 cos d: sin 0 sin cos 0) Bottom SW (12/8) +j (C/8)(sin 6 cos d: sin 0 sin cos 0) Bottom NW (R/8) +j (C/8) (sin 0 cos 11sin 0 sin (I) cos 6) 7 As previously mentioned, the circumferentialvibration mode is degenerate in three degrees of freedom so that itscomponent magnitude C must be modified by the angular projection interms of sines and cosines of (b and 6. Note that the circumferentialcomponents of opposite octants such as Top SE and Bottom NW are 180 outof phase.

The summing circuit is organized in a manner substantially according toUS. Pat. No. 3,176,262 such that the resultant sum signals appearing onlines 88, 9t), 92, and 96 may be algebraically represented also by acomplex quantity having orthogonal components. To this extent, the eightindependent signals applied to the summing circuits are reduced to fouroutput signals from the summing circuits; Three of the outputs aredesignated as geographical, such as NS (north south), EW (east west), TB(top bottom). The fourth signal designated by omniphase reference isapplied on path 96. The resultant sum signals NS, EW, TB, and OMNI maybe represented as:

NS (TNE-i-BNE) (TNW+BNW) (TSE+BSE) (TSW+BSW) =j C sin 6 cos 4:

EW (TNE+BNE) (TNW-FBNW) (TSE-i-BSE) (TSW+BSW) ==j Csin 0 sin d:

TB (TNE-BNE) (TNW-BNW) (TSE-BSE) (TSW-BSW) =j C cos 6 OMNl (TNE+BNE)(TNW+BNW) (TSE+BSE) (TSW+BSE) R It should be observed that thetransducer 50 is divided into equal area octant segments havingpositioned thereon a corresponding one of the surface electrodes 102,104, 106, 108, 110, 112, 114, and 116. The radial or circumferentialvibration will induce voltages on corresponding paths 54 through 68which in turn will be summed by summing circuits 86 throughcorresponding amplifiers 70 through 84. The summing circuits effectivelyalgebraically combine the eight signals applied thereto to produce fouroutput signals. As is apparent from the mathematical exposition of theresultant sum signals, each said sum signal is formed from a portion orcontribution of each of the eight input signals.

Attention is directed to US. Pat. Nos. 3,176,262 and 3,290,646 for adetailed discussion of the construction of the summing circuits.

The present invention has been described for use as an underwateracoustic receiver and by analytic extension as an acoustic transmitter.It is contemplated that such transducer is useful in environments otherthan water where compression wave energy may be utilized to vibrate sucha transducer as, for example, in gas or air. it is realized thatmodifications may be made, and it is desired that it be understood thatno limitations on the invention are intended other than may be imposedby the scope of the appended claims.

I claim:

1. An acoustic transducer comprising:

a spherical shell formed from electromechanically active material;

a plurality of electrodes attached to the shell outer surface andregularly spaced over equal area segments thereof;

an electrode connected to the shell inner surface to provide a commonvoltage reference point; and

combining means coupling the outer electrodes and the inner electrodefor generating at least one dipole voltage upon vibration of thespherical shell.

2. An acoustic transducer according to claim 1, in which the combiningmeans generates n orthogonally phased dipole voltages and anomnidirectional pattern voltage upon vibration of the spherical shell.

3. An acoustic transducer comprising:

a spherical shell formed from electromechanically active material;

a plurality of electrodes attached to the shell outer surface and evenlydistributed thereover for detecting the electrical manifestations ofradial mode and circumferential mode vibration inducible in thespherical shell;

an electrode attached to the shell inner surface for providing a commonvoltage reference point; and

combining means coupling the outer electrodes and the inner electrodefor generating at least two orthogonally phased dipole voltages uponvibration of the spherical shell.

. An acoustic transducer comprising:

spherical shell formed from electromechanically active material andhaving its elemental surface area boundaries joined at a common metalliclocus, the metallic locus serving as a common voltage reference line;

a plurality of electrodes attached to the shell outer surface andregularly spaced over equal area segments thereof; and

combining means coupling the electrodes and the metallic locus forgenerating an output dipole voltage upon vibration of the sphericalshell.

5. An acoustic transducer according to claim 4,

wherein the elemental surface areas form hemispheres.

6. An acoustic transducer comprising:

a spherical shell formed from electromechanically active material anddivided into a plurality of elemental surface areas;

a plurality of electrodes attached to the shell outer surface anddistributed such that a pair of electrically insulated electrodes isassigned to each elemental area, one electrode of each pair'serving as areference voltage point thereof;

a common electrode attached to the shell inner surface for maintaining asubstantially radial electric field; and

combining means coupling the electrode pairs for generating a dipolevoltage upon vibration of the spherical shell.

7. An acoustic transducer according to claim 6, wherein the plurality ofelemental surface areas consists of octant segments.

8. An acoustic transducer according to claim 6, wherein the commonelectrode reduces the inter-electrode capacitance between each surfaceelectrode pair.

9. An acoustic transducer according to claim 6, wherein the referencevoltage point electrode of each pair is connected together to form acommon ground.

10. An acoustic transducer according to claim 6, wherein the referencevoltage point electrodes of each pair are connected in predeterminedconnectable groups.

11. An acoustic transducer according to claim 6, wherein the transducerincludes means for applying a positive biasing voltage to the remainingelectrode of each pair.

12. An acoustic transducer according to claim 6, wherein theelectromechanically active material is selected from the group ofpiezoelectric material.

13. An acoustic transducer according to claim 6, wherein theelectromechanically active material is selected from the group ofmagnetostrictive materials.

14. An acoustic system comprising:

a transducer body comprising a shell having an outer radiating surfacecurved about a plurality of mutually orthogonal axes and an innersurface;

a plurality of electrical means coupled respectively to differentregions of at least one of said surfaces of said body;

each of said regions extending for a sufficient distance to provide forsubstantial curvature along said surface in all directions;

means for coupling a voltage reference to the other of said surfaces;

signal combinin means and means for coup mg different phase signalsbetween said combining means and said plurality of electrical meanscoupled to said body.

15. The system in accordance with claim 14 in which said combining meansare coupled with said plurality of electrical means coupled respectivelyto different regions of said body in a format which generates at least aplurality of radiation patterns along different axes.

16. The system in accordance with claim 14 in which the combining meansgenerate an orthogonally phased dipole voltage and an omnidirectionalpattern voltage.

17. The system in accordance with claim 15 in which at least a pluralityof said radiation patterns are directive.

1. An acoustic transducer comprising: a spherical shell formed fromelectromechanically active material; a plurality of electrodes attachedto the shell outer surface and regularly spaced over equal area segmentsthereof; an electrode connected to the shell inner surface to provide acommon voltage reference point; and combining means coupling the outerelectrodes and the inner electrode for generating at least one dipolevoltage upon vibration of the spherical shell.
 2. An acoustic transduceraccording to claim 1, in which the combining means generates northogonally phased dipole voltages and an omnidirectional patternvoltage upon vibration of the spherical shell.
 3. An acoustic transducercomprising: a spherical shell formed from electromechanically activematerial; a plurality of electrodes attached to the shell outer surfaceand evenly distributed thereover for detecting the electricalmanifestations of radial mode and circumferential mode vibrationinducible in the spherical shell; an electrode attached to the shellinner surface for providing a common voltage reference point; andcombining means coupling the outer electrodes and the inner electrodefor generating at least two orthogonally phased dipole voltages uponvibration of the spherical shell.
 4. An acoustic transducer comprising:a spherical shell formed from electromechanically active material andhaving its elemental surface area boundaries joined at a common metalliclocus, the metallic locus serving as a common voltage reference line; aplurality of electrodes attached to the shell outer surface andregularly spaced over equal area segments thereof; and combining meanscoupling the electrodes and the metallic locus for generating an outputdipole voltage upon vibration of the spherical shell.
 5. An acoustictransducer according to claim 4, wherein the elemental surface areasform hemispheres.
 6. An acoustic transducer comprising: a sphericalshell formed from electromechanically active material and divided into aplurality of elemental surface areas; a plurality of electrodes attachedto the shell outer surface and distributed such that a pair ofelectrically insulated electrodes is assigned to each elemental area,one electrode of each pair serving as a reference voltage point thereof;a common electrode attached to the shell inner surface for maintaining asubstantially radial electric field; and combining means coupling theelectrode pairs for generating a dipole voltage upon vibration of thespherical shell.
 7. An acoustic transducer according to claim 6, whereinthe plurality of elemental surface areas consists of octant segments. 8.An acoustic transducer according to claim 6, wherein the commonelectrode reduces the inter-electrode capacitance between each surfaceelectrode pair.
 9. An acoustic transducer according to claim 6, whereinthe reference voltage point electrode of each pair is connected togetherto form a common ground.
 10. An acoustic transducer according to claim6, wherein the reference voltage point electrodes of each pair areconnected in predetermined connectable groups.
 11. An acoustictransducer according to claim 6, wherein the transducer includes meansfor applying a positive biasing voltage to the remaining electrode ofeach pair.
 12. An acoustic transducer according to claim 6, wherein theelectromechanically active material is selected from the group ofpiezoelectric material.
 13. An acoustic transducer according to claim 6,wherein the electromechanically active material is selected from thegroup of magnetostrictive materials.
 14. An acoustic system comprising:a transducer body comprising a shell having an outer radiating surfacecurved about a plurality of mutually orthogonal axes and an innersurface; a plurality of electrical means coUpled respectively todifferent regions of at least one of said surfaces of said body; each ofsaid regions extending for a sufficient distance to provide forsubstantial curvature along said surface in all directions; means forcoupling a voltage reference to the other of said surfaces; signalcombining means; and means for coupling different phase signals betweensaid combining means and said plurality of electrical means coupled tosaid body.
 15. The system in accordance with claim 14 in which saidcombining means are coupled with said plurality of electrical meanscoupled respectively to different regions of said body in a format whichgenerates at least a plurality of radiation patterns along differentaxes.
 16. The system in accordance with claim 14 in which the combiningmeans generate an orthogonally phased dipole voltage and anomnidirectional pattern voltage.
 17. The system in accordance with claim15 in which at least a plurality of said radiation patterns aredirective.